An example of a prior-art musical tone generator system of the type to which the present invention generally appertains is disclosed in Japanese Utility Model Specification No. 59-18471. The musical tone generator system therein taught includes a plurality of percussive tone source circuits which correspond in number to the percussive tones of different types of percussion instruments available. Pulses representative of rhythm tones of different ones of the percussion instruments are read out at predetermined timings from a rhythm pattern memory and are respectively supplied to these percussive tone source circuits each via one input terminal of an OR gate. To the other input terminal of each of the OR gates thus respectively associated with the percussive tone source circuits pulses produced with tone select keys manually activated on the control board of the system. Not only the rhythm tones dictated by the data read from the rhythm pattern memory are generated in an automatic fashion but the percussive tones selected by the player manipulating the control board can be generated by this type of musical tone generator system.
Another example of a known musical tone generator system of the type with which the present invention is concerned is disclosed in U.S. Pat. No. 4,467,690. In the musical tone generator system disclosed therein are provided percussive tone source circuits which are smaller in number than the tones of the percussion instruments available. The number of the kinds of percussive tones to be generated for each of the rhythm patterns for march, waltz and so forth is limited to be equal to the number of the percussive tone source circuits provided in the system. Pulses representative of different kinds of rhythm tones are respectively supplied to these percussive tone source circuits to generate tones of different percussion instruments for each of the rhythm patterns used.
A prior-art musical tone generator system of the former type has a drawback in that it is required to provide percussive tone source circuits which are equal in number to the kinds of percussive tones available. It being desirable that there are available tones of as large number of types of percussion instruments as possible, provision of such a number of percussive tone source circuit results in an increase in the production cost of the system.
Such a drawback is eliminated in a known musical tone generator system of the latter type in which the number of the percussive tone source circuits may be less than the number of the kinds of percussive tones available. In this type of prior-art musical tone generator system, however, a problem is encountered when the player desires to add musical tones to a sequence of tones automatically generated in a given rhythm pattern. Tones of only a limited number of percussion instruments being available, the player may not be permitted to use his desired kinds of tones.
The present invention contemplates elimination of these drawbacks of known types of musical tone generator system. It is, accordingly, an important object of the present invention to reduce the production cost and provide an increased range of selection of percussive tones in a musical tone generator system capable of generating a sequence of musical tones in a rhythm pattern determined in accordance with a rhythm pattern data fetched from a rhythm pattern memory accompanied by generation of musical tones designated from manually operated tone select keys.
A third type of known musical tone generator system is taught in U.S. Pat. No. 4,041,826. In the musical tone generator system disclosed therein, the individual tone select keys on the control board are respectively allocated to different tone signal forming channels. Each time a tone select key is manually depressed and thereafter released and accordingly a tone is generated and then attenuated, counts produced in conjunction with the tone signal forming channels corresponding to the tone select keys which have already been released from manipulative efforts are incremented indiscriminately for these channels. The order in which the tone select keys have been released can thus be indicated by the respective counts for the individual signal forming channels. The counts for the tone signal forming channels are then compared together to detect the channel associated with the largest count and accordingly corresponding to the earliest activated tone select key. A newly activated tone select key is allocated to the channel thus detected so that the tone designated by the newly activated tone select key is to be generated through this particular tone signal forming channel.
There is a fourth type of prior-art musical tone generator system, an example of which is disclosed in U.S. Pat. No. 4,114,495. In the musical tone generator system proposed therein, envelopes are produced for the control of volume levels of the tones to be generated through different tone signal forming channels. From among these signal forming channels, the channel corresponding to the volume control envelope having the smallest amplitude indicating the lowest volume level is detected. A newly activated tone select key is allocated to the signal forming channel thus detected so that the tone designated by the newly activated tone select key is to be generated through this particular tone signal forming channel.
A prior-art musical tone generator system of the third type has a drawback which results from the fact that tone select keys newly activated are allocated to any of the tone signal forming channels in an order in which the tone select keys have been released from manipulative efforts. Such an order being irrespective of the attenuation periods viz., the durations of tones generated, a problem arises which is however not encountered when the tones concurrently generated have equal attenuation periods. The problem is that, when tones including a tone having a relatively short attenuation period and a tone having a relatively long attenuation period are to be generated simultaneously, generation of the tone having the long attenuation period may be terminated earlier than the tone having the short attenuation period although the generation of the tone having the long attenuation period is incomplete. For this reason, the prior-art musical tone generator system of the third type is not suitable for the concurrent generation of different kinds of musical tones.
A drawback in a conventional musical tone generator system of the fourth type is that provision of some extra circuits are required. Such additional circuits include a circuit to search for the channel corresponding to the volume control envelope having the smallest amplitude indicating the lowest volume level is detected, a circuit for detecting the amplitude of the volume control envelope and producing a signal indicative of the detected amplitude, and a circuit for transferring the signal to the channel allocation control circuit. The provision of these extra circuits will significantly add to the production cost of the system.
It is accordingly a second important object of the present invention to reduce the production cost and enable improved channel allocation of percussive tones in a musical tone generator system capable of generating a sequence of musical tones in a rhythm pattern determined in accordance with a rhythm pattern data fetched from a rhythm pattern memory accompanied by generation of musical tones designated from manually operated tone select keys.
In a prior-art musical tone generator system of the type disclosed in Japanese Utility Model Specification No. 59-18471 as previously mentioned, there is another problem that, when percussive tones are generated by manipulation of the tone select keys with the automatically controlled mode of rhythmation selected, tones are generated with the automatically controlled rhythmation in addition to the tones resulting from the manipulation of the tone select keys. Thus, the player of the system is not permitted to introduce tones with manually controlled rhythmation into the sequence of tones being generated with the automatically controlled rhythmation. Such a problem could be solved if switches to start and terminate the automatically controlled rhythmation are manipulated to interrupt the automatically controlled mode of rhythmation to enable the player to produce tones through manipulation of the tone select keys. This however imposes added burdens on the player in manipulating the switches in addition to the tone select keys. A further object of the present invention is to provide a musical tone generator system free from this problem.